class Gtk::Builder

Overview

A Gtk::Builder reads XML descriptions of a user interface and instantiates the described objects.

To create a Gtk::Builder from a user interface description, call Gtk::Builder#new_from_file, Gtk::Builder#new_from_resource or Gtk::Builder#new_from_string.

In the (unusual) case that you want to add user interface descriptions from multiple sources to the same Gtk::Builder you can call Gtk::Builder.new to get an empty builder and populate it by (multiple) calls to Gtk::Builder#add_from_file, Gtk::Builder#add_from_resource or Gtk::Builder#add_from_string.

A Gtk::Builder holds a reference to all objects that it has constructed and drops these references when it is finalized. This finalization can cause the destruction of non-widget objects or widgets which are not contained in a toplevel window. For toplevel windows constructed by a builder, it is the responsibility of the user to call Gtk::Window#destroy to get rid of them and all the widgets they contain.

The functions Gtk::Builder#object and Gtk::Builder#objects can be used to access the widgets in the interface by the names assigned to them inside the UI description. Toplevel windows returned by these functions will stay around until the user explicitly destroys them with Gtk::Window#destroy. Other widgets will either be part of a larger hierarchy constructed by the builder (in which case you should not have to worry about their lifecycle), or without a parent, in which case they have to be added to some container to make use of them. Non-widget objects need to be reffed with g_object_ref() to keep them beyond the lifespan of the builder.

Gtk::Builder UI Definitions

Gtk::Builder parses textual descriptions of user interfaces which are specified in XML format. We refer to these descriptions as “Gtk::Builder UI definitions” or just “UI definitions” if the context is clear.

The toplevel element is <interface>. It optionally takes a “domain” attribute, which will make the builder look for translated strings using dgettext() in the domain specified. This can also be done by calling Gtk::Builder#translation_domain= on the builder.

Objects are described by <object> elements, which can contain <property> elements to set properties, <signal> elements which connect signals to handlers, and <child> elements, which describe child objects (most often widgets inside a container, but also e.g. actions in an action group, or columns in a tree model). A <child> element contains an <object> element which describes the child object.

The target toolkit version(s) are described by <requires> elements, the “lib” attribute specifies the widget library in question (currently the only supported value is “gtk”) and the “version” attribute specifies the target version in the form “<major>.<minor>”. Gtk::Builder will error out if the version requirements are not met.

Typically, the specific kind of object represented by an <object> element is specified by the “class” attribute. If the type has not been loaded yet, GTK tries to find the get_type() function from the class name by applying heuristics. This works in most cases, but if necessary, it is possible to specify the name of the get_type() function explicitly with the "type-func" attribute.

Objects may be given a name with the “id” attribute, which allows the application to retrieve them from the builder with Gtk::Builder#object. An id is also necessary to use the object as property value in other parts of the UI definition. GTK reserves ids starting and ending with ___ (three consecutive underscores) for its own purposes.

Setting properties of objects is pretty straightforward with the <property> element: the “name” attribute specifies the name of the property, and the content of the element specifies the value. If the “translatable” attribute is set to a true value, GTK uses gettext() (or dgettext() if the builder has a translation domain set) to find a translation for the value. This happens before the value is parsed, so it can be used for properties of any type, but it is probably most useful for string properties. It is also possible to specify a context to disambiguate short strings, and comments which may help the translators.

Gtk::Builder can parse textual representations for the most common property types: characters, strings, integers, floating-point numbers, booleans (strings like “TRUE”, “t”, “yes”, “y”, “1” are interpreted as true, strings like “FALSE”, “f”, “no”, “n”, “0” are interpreted as false), enumerations (can be specified by their name, nick or integer value), flags (can be specified by their name, nick, integer value, optionally combined with “|”, e.g. “GTK_INPUT_HINT_EMOJI|GTK_INPUT_HINT_LOWERCASE”) and colors (in a format understood by Gdk::RGBA#parse).

GVariants can be specified in the format understood by g_variant_parse(), and pixbufs can be specified as a filename of an image file to load.

Objects can be referred to by their name and by default refer to objects declared in the local XML fragment and objects exposed via Gtk::Builder#expose_object. In general, Gtk::Builder allows forward references to objects — declared in the local XML; an object doesn’t have to be constructed before it can be referred to. The exception to this rule is that an object has to be constructed before it can be used as the value of a construct-only property.

It is also possible to bind a property value to another object's property value using the attributes "bind-source" to specify the source object of the binding, and optionally, "bind-property" and "bind-flags" to specify the source property and source binding flags respectively. Internally, Gtk::Builder implements this using GBinding objects. For more information see g_object_bind_property().

Sometimes it is necessary to refer to widgets which have implicitly been constructed by GTK as part of a composite widget, to set properties on them or to add further children (e.g. the content area of a Gtk::Dialog). This can be achieved by setting the “internal-child” property of the <child> element to a true value. Note that Gtk::Builder still requires an <object> element for the internal child, even if it has already been constructed.

A number of widgets have different places where a child can be added (e.g. tabs vs. page content in notebooks). This can be reflected in a UI definition by specifying the “type” attribute on a <child> The possible values for the “type” attribute are described in the sections describing the widget-specific portions of UI definitions.

Signal handlers and function pointers

Signal handlers are set up with the <signal> element. The “name” attribute specifies the name of the signal, and the “handler” attribute specifies the function to connect to the signal. The remaining attributes, “after”, “swapped” and “object”, have the same meaning as the corresponding parameters of the g_signal_connect_object() or g_signal_connect_data() functions. A “last_modification_time” attribute is also allowed, but it does not have a meaning to the builder.

If you rely on GModule support to lookup callbacks in the symbol table, the following details should be noted:

When compiling applications for Windows, you must declare signal callbacks with %G_MODULE_EXPORT, or they will not be put in the symbol table. On Linux and Unix, this is not necessary; applications should instead be compiled with the -Wl,--export-dynamic CFLAGS, and linked against gmodule-export-2.0.

A Gtk::Builder UI Definition

WARNING ⚠️ The following code is in xml ⚠️

<interface>
  <object class="Gtk::Dialog" id="dialog1">
    <child internal-child="content_area">
      <object class="Gtk::Box" id="vbox1">
        <child internal-child="action_area">
          <object class="Gtk::Box" id="hbuttonbox1">
            <child>
              <object class="Gtk::Button" id="ok_button">
                <property name="label" translatable="yes">_Ok</property>
                <property name="use-underline">True</property>
                <signal name="clicked" handler="ok_button_clicked"/>
              </object>
            </child>
          </object>
        </child>
      </object>
    </child>
  </object>
</interface>

Beyond this general structure, several object classes define their own XML DTD fragments for filling in the ANY placeholders in the DTD above. Note that a custom element in a element gets parsed by the custom tag handler of the parent object, while a custom element in an element gets parsed by the custom tag handler of the object.

These XML fragments are explained in the documentation of the respective objects.

A <template> tag can be used to define a widget class’s components. See the Gtk::Widget documentation for details.

Defined in:

lib/gi-crystal/src/auto/gtk-4.0/builder.cr
lib/gtk4/src/bindings/gtk/builder.cr

Constructors

Class Method Summary

Instance Method Summary

Instance methods inherited from class GObject::Object

bind_property(source_property : String, target : GObject::Object, target_property : String, flags : GObject::BindingFlags) : GObject::Binding bind_property, bind_property_full(source_property : String, target : GObject::Object, target_property : String, flags : GObject::BindingFlags, transform_to : GObject::Closure, transform_from : GObject::Closure) : GObject::Binding bind_property_full, data(key : String) : Pointer(Void)? data, finalize finalize, freeze_notify : Nil freeze_notify, getv(names : Enumerable(String), values : Enumerable(_)) : Nil getv, notify(property_name : String) : Nil notify, notify_by_pspec(pspec : GObject::ParamSpec) : Nil notify_by_pspec, notify_signal notify_signal, property(property_name : String, value : _) : Nil property, qdata(quark : UInt32) : Pointer(Void)? qdata, ref_count : UInt32 ref_count, run_dispose : Nil run_dispose, set_data(key : String, data : Pointer(Void)?) : Nil set_data, set_property(property_name : String, value : _) : Nil set_property, steal_data(key : String) : Pointer(Void)? steal_data, steal_qdata(quark : UInt32) : Pointer(Void)? steal_qdata, thaw_notify : Nil thaw_notify, to_unsafe : Pointer(Void) to_unsafe, watch_closure(closure : GObject::Closure) : Nil watch_closure

Constructor methods inherited from class GObject::Object

cast(obj : GObject::Object) : self cast, cast?(obj : GObject::Object) : self? cast?, new(pointer : Pointer(Void), transfer : GICrystal::Transfer)
new new, newv(object_type : UInt64, parameters : Enumerable(GObject::Parameter)) : self newv

Class methods inherited from class GObject::Object

compat_control(what : UInt64, data : Pointer(Void)?) : UInt64 compat_control, g_type : UInt64 g_type, interface_find_property(g_iface : GObject::TypeInterface, property_name : String) : GObject::ParamSpec interface_find_property, interface_list_properties(g_iface : GObject::TypeInterface) : Enumerable(GObject::ParamSpec) interface_list_properties

Constructor Detail

def self.new : self #

Creates a new empty builder object.

This function is only useful if you intend to make multiple calls to Gtk::Builder#add_from_file, Gtk::Builder#add_from_resource or Gtk::Builder#add_from_string in order to merge multiple UI descriptions into a single builder.


def self.new(*, current_object : GObject::Object? = nil, scope : Gtk::BuilderScope? = nil, translation_domain : String? = nil) #

def self.new_from_file(filename : String) : self #

Parses the UI definition in the file @filename.

If there is an error opening the file or parsing the description then the program will be aborted. You should only ever attempt to parse user interface descriptions that are shipped as part of your program.


def self.new_from_resource(resource_path : String) : self #

Parses the UI definition at @resource_path.

If there is an error locating the resource or parsing the description, then the program will be aborted.


def self.new_from_string(string : String, length : Int64) : self #

Parses the UI definition in @string.

If @string is nil-terminated, then @length should be -1. If @length is not -1, then it is the length of @string.

If there is an error parsing @string then the program will be aborted. You should not attempt to parse user interface description from untrusted sources.


Class Method Detail

def self.g_type : UInt64 #

Returns the type id (GType) registered in GLib type system.


Instance Method Detail

def add_from_file(filename : String) : Bool #

Parses a file containing a UI definition and merges it with the current contents of @builder.

This function is useful if you need to call Gtk::Builder#current_object=) to add user data to callbacks before loading Gtk::Builder UI. Otherwise, you probably want Gtk::Builder#new_from_file instead.

If an error occurs, 0 will be returned and @error will be assigned a GError from the GTK_BUILDER_ERROR, G_MARKUP_ERROR or G_FILE_ERROR domains.

It’s not really reasonable to attempt to handle failures of this call. You should not use this function with untrusted files (ie: files that are not part of your application). Broken Gtk::Builder files can easily crash your program, and it’s possible that memory was leaked leading up to the reported failure. The only reasonable thing to do when an error is detected is to call g_error().


def add_from_resource(resource_path : String) : Bool #

Parses a resource file containing a UI definition and merges it with the current contents of @builder.

This function is useful if you need to call Gtk::Builder#current_object= to add user data to callbacks before loading Gtk::Builder UI. Otherwise, you probably want Gtk::Builder#new_from_resource instead.

If an error occurs, 0 will be returned and @error will be assigned a GError from the %GTK_BUILDER_ERROR, %G_MARKUP_ERROR or %G_RESOURCE_ERROR domain.

It’s not really reasonable to attempt to handle failures of this call. The only reasonable thing to do when an error is detected is to call g_error().


def add_from_string(buffer : String, length : Int64) : Bool #

Parses a string containing a UI definition and merges it with the current contents of @builder.

This function is useful if you need to call Gtk::Builder#current_object= to add user data to callbacks before loading Gtk::Builder UI. Otherwise, you probably want Gtk::Builder#new_from_string instead.

Upon errors false will be returned and @error will be assigned a GError from the %GTK_BUILDER_ERROR, %G_MARKUP_ERROR or %G_VARIANT_PARSE_ERROR domain.

It’s not really reasonable to attempt to handle failures of this call. The only reasonable thing to do when an error is detected is to call g_error().


def add_objects_from_file(filename : String, object_ids : Enumerable(String)) : Bool #

Parses a file containing a UI definition building only the requested objects and merges them with the current contents of @builder.

Upon errors, 0 will be returned and @error will be assigned a GError from the %GTK_BUILDER_ERROR, %G_MARKUP_ERROR or %G_FILE_ERROR domain.

If you are adding an object that depends on an object that is not its child (for instance a Gtk::TreeView that depends on its Gtk::TreeModel), you have to explicitly list all of them in @object_ids.


def add_objects_from_resource(resource_path : String, object_ids : Enumerable(String)) : Bool #

Parses a resource file containing a UI definition, building only the requested objects and merges them with the current contents of @builder.

Upon errors, 0 will be returned and @error will be assigned a GError from the %GTK_BUILDER_ERROR, %G_MARKUP_ERROR or %G_RESOURCE_ERROR domain.

If you are adding an object that depends on an object that is not its child (for instance a Gtk::TreeView that depends on its Gtk::TreeModel), you have to explicitly list all of them in @object_ids.


def add_objects_from_string(buffer : String, length : Int64, object_ids : Enumerable(String)) : Bool #

Parses a string containing a UI definition, building only the requested objects and merges them with the current contents of @builder.

Upon errors false will be returned and @error will be assigned a GError from the %GTK_BUILDER_ERROR or %G_MARKUP_ERROR domain.

If you are adding an object that depends on an object that is not its child (for instance a Gtk::TreeView that depends on its Gtk::TreeModel), you have to explicitly list all of them in @object_ids.


def create_closure(function_name : String, flags : Gtk::BuilderClosureFlags, object : GObject::Object?) : GObject::Closure? #

Creates a closure to invoke the function called @function_name.

This is using the create_closure() implementation of @builder's Gtk::BuilderScope.

If no closure could be created, nil will be returned and @error will be set.


def current_object : GObject::Object? #

Gets the current object set via gtk_builder_set_current_object().


def current_object=(current_object : GObject::Object?) : Nil #

Sets the current object for the @builder.

The current object can be thought of as the this object that the builder is working for and will often be used as the default object when an object is optional.

Gtk::Widget#init_template for example will set the current object to the widget the template is inited for. For functions like Gtk::Builder#new_from_resource, the current object will be nil.


def expose_object(name : String, object : GObject::Object) : Nil #

Add @object to the @builder object pool so it can be referenced just like any other object built by builder.

Only a single object may be added using @name. However, it is not an error to expose the same object under multiple names. gtk_builder_get_object() may be used to determine if an object has already been added with @name.


def extend_with_template(object : GObject::Object, template_type : UInt64, buffer : String, length : Int64) : Bool #

Main private entry point for building composite components from template XML.

Most likely you do not need to call this function in applications as templates are handled by Gtk::Widget.


def object(name : String) : GObject::Object? #

Gets the object named @name.

Note that this function does not increment the reference count of the returned object.


def objects : GLib::SList #

Gets all objects that have been constructed by @builder.

Note that this function does not increment the reference counts of the returned objects.


def scope : Gtk::BuilderScope #

Gets the scope in use that was set via gtk_builder_set_scope().


def scope=(scope : Gtk::BuilderScope?) : Nil #

Sets the scope the builder should operate in.

If @scope is nil, a new Gtk::BuilderCScope will be created.


def translation_domain : String? #

Gets the translation domain of @builder.


def translation_domain=(value : String) : String #

def translation_domain=(domain : String?) : Nil #

Sets the translation domain of @builder.


def type_from_name(type_name : String) : UInt64 #

Looks up a type by name.

This is using the virtual function that Gtk::Builder has for that purpose. This is mainly used when implementing the Gtk::Buildable interface on a type.


def value_from_string(pspec : GObject::ParamSpec, string : String) : GObject::Value #

Demarshals a value from a string.

This function calls g_value_init() on the @value argument, so it need not be initialised beforehand.

Can handle char, uchar, boolean, int, uint, long, ulong, enum, flags, float, double, string, Gdk::RGBA and Gtk::Adjustment type values.

Upon errors false will be returned and @error will be assigned a GError from the %GTK_BUILDER_ERROR domain.


def value_from_string_type(type : UInt64, string : String) : GObject::Value #

Demarshals a value from a string.

Unlike Gtk::Builder#value_from_string, this function takes a GType instead of GParamSpec.

Calls g_value_init() on the @value argument, so it need not be initialised beforehand.

Upon errors false will be returned and @error will be assigned a GError from the %GTK_BUILDER_ERROR domain.